# Custom Summary | WPF Controls | DevExpress Documentation [Total summaries](/WPF/6128/controls-and-libraries/data-grid/data-summaries/total-summary) and [group summaries](/WPF/6127/controls-and-libraries/data-grid/data-summaries/group-summary) contain predefined aggregate functions. These functions allow you to calculate the following: - The number of data rows (**Count**). - The maximum and minimum values (**Max** and **Min**). - The sum and the average value (**Sum** and **Average**). Handle the [GridControl.CustomSummary](/WPF/DevExpress.Xpf.Grid.GridControl.CustomSummary) event or use the [GridControl.CustomSummaryCommand](/WPF/DevExpress.Xpf.Grid.GridControl.CustomSummaryCommand) property to apply custom rules to calculate summaries. Custom summaries allow you to: - Calculate summaries against records that meet specific criteria. - Involve multiple data fields in calculations. - Implement complex summary functions (for example, the standard deviation of a population and so on). If the [GridControl.View](/WPF/DevExpress.Xpf.Grid.GridControl.View) property is set to [TreeListView](/WPF/DevExpress.Xpf.Grid.TreeListView), use the [TreeListView.CustomSummary](/WPF/DevExpress.Xpf.Grid.TreeListView.CustomSummary) event or the [TreeListView.CustomSummaryCommand](/WPF/DevExpress.Xpf.Grid.TreeListView.CustomSummaryCommand) property. ## General Information To calculate a summary manually: 1. Create a summary item and set its [SummaryItemBase.SummaryType](/WPF/DevExpress.Xpf.Grid.SummaryItemBase.SummaryType) property to [SummaryItemType.Custom](/CoreLibraries/DevExpress.Data.SummaryItemType). 2. Create a command that uses a custom algorithm to calculate summary values. 3. Bind this command to the [GridControl.CustomSummaryCommand](/WPF/DevExpress.Xpf.Grid.GridControl.CustomSummaryCommand) property. The [GridControl](/WPF/DevExpress.Xpf.Grid.GridControl) calculates its summaries as follows: - Initialization - The GridControl executes the **CustomSummary** command and sets the [SummaryArgs.SummaryProcess](/CoreLibraries/DevExpress.Mvvm.Xpf.SummaryArgs.SummaryProcess) property to **Start**. At this stage, you can initialize summary values (for example, reset internal counters). - Calculation - The GridControl executes the **CustomSummary** command multiple times, once for each data row in a View or group. The [SummaryArgs.SummaryProcess](/CoreLibraries/DevExpress.Mvvm.Xpf.SummaryArgs.SummaryProcess) property is set to **Calculate**. At this stage, you can calculate summaries. - Finalization - The GridControl executes the **CustomSummary** command and sets the [SummaryArgs.SummaryProcess](/CoreLibraries/DevExpress.Mvvm.Xpf.SummaryArgs.SummaryProcess) property to **Finalize**. At this stage, you can assign the calculated summary to the [SummaryArgs.TotalValue](/CoreLibraries/DevExpress.Mvvm.Xpf.SummaryArgs.TotalValue) property. To skip the **Calculation** stage and calculate a custom summary at the **Initialization** or **Finalization** stage, set the [SummaryArgs.TotalValueReady](/CoreLibraries/DevExpress.Mvvm.Xpf.SummaryArgs.TotalValueReady) property to **true** at the Initialization stage. This skips the **Calculation** stage and starts the **Finalization** stage. ## Calculate Custom Summaries The following code sample calculates the total number of empty cells in the specified column: ![DevExpress WPF | Grid Control - Custom Summaries](/WPF/images/GridControl_CustomSummaryCommand.png) [View Example: How to Use Custom Summaries](https://github.com/DevExpress-Examples/wpf-data-grid-summarize-empty-cells) - MainWindow.xaml

<dxg:GridControl ItemsSource="{Binding Items}"
                 CustomSummaryCommand="{Binding CustomSummaryCommand}">
    <dxg:GridControl.Columns>
        <dxg:GridColumn FieldName="Text" GroupIndex="0" />
        <dxg:GridColumn FieldName="Number" />
    </dxg:GridControl.Columns>
    <dxg:GridControl.View>
        <dxg:TableView AutoWidth="True"
                       NavigationStyle="Cell"
                       TotalSummaryPosition="Bottom" />
    </dxg:GridControl.View>
    <dxg:GridControl.TotalSummary>
        <dxg:GridSummaryItem DisplayFormat="Total empty cells count: {0}"
                             FieldName="Number"
                             SummaryType="Custom" />
    </dxg:GridControl.TotalSummary>
    <dxg:GridControl.GroupSummary>
        <dxg:GridSummaryItem DisplayFormat="Group empty cells count: {0}"
                             FieldName="Number"
                             SummaryType="Custom" />
    </dxg:GridControl.GroupSummary>
</dxg:GridControl>

- MainViewModel.cs - MainViewModel.vb

using DevExpress.Mvvm;
using DevExpress.Mvvm.DataAnnotations;
using DevExpress.Mvvm.Xpf;
// ...
public class MainViewModel : ViewModelBase {
// ...
    [Command]
    public void CustomSummary(RowSummaryArgs args) {
        if(args.SummaryItem.PropertyName != "Number")
            return;
        if(args.SummaryProcess == SummaryProcess.Start) {
            args.TotalValue = 0;
        } 
        if(args.SummaryProcess == SummaryProcess.Calculate) {
            if(IsEmptyCell(args.FieldValue))
                args.TotalValue = (int)args.TotalValue + 1;
        }
    }
    bool IsEmptyCell(object fieldValue) {
        return !((int?)fieldValue).HasValue;
    }
}

Imports DevExpress.Mvvm
Imports DevExpress.Mvvm.DataAnnotations
Imports DevExpress.Mvvm.Xpf
' ...
Public Class MainViewModel
    Inherits ViewModelBase
' ...
    <Command>
    Public Sub CustomSummary(ByVal args As RowSummaryArgs)
        If Not Equals(args.SummaryItem.PropertyName, "Number") Then Return
        If args.SummaryProcess = SummaryProcess.Start Then
            args.TotalValue = 0
        End If

        If args.SummaryProcess = SummaryProcess.Calculate Then
            If IsEmptyCell(args.FieldValue) Then args.TotalValue = CInt(args.TotalValue) + 1
        End If
    End Sub

    Private Function IsEmptyCell(ByVal fieldValue As Object) As Boolean
        Return Not CType(fieldValue, Integer?).HasValue
    End Function
End Class

## Calculate Custom Summaries Based on Predefined Summaries The [GridControl](/WPF/DevExpress.Xpf.Grid.GridControl) calculates custom summaries after predefined summaries (**Count**, **Sum**, **Min**, and so on). As a result, you can use predefined summary values to calculate custom summaries: 1. Create a custom summary. 2. Handle the [GridControl.CustomSummary](/WPF/DevExpress.Xpf.Grid.GridControl.CustomSummary) / [TreeListView.CustomSummary](/WPF/DevExpress.Xpf.Grid.TreeListView.CustomSummary) event. 3. At the **Initialization** stage, set the [e.TotalValueReady](/CoreLibraries/DevExpress.Data.CustomSummaryEventArgs.TotalValueReady) property to `true` to skip the **Calculation** stage. 4. Use the [DataControlBase.GetTotalSummaryValue](/WPF/DevExpress.Xpf.Grid.DataControlBase.GetTotalSummaryValue%28DevExpress.Xpf.Grid.SummaryItemBase%29) method to obtain predefined summaries at the **Finalization** stage. ![Calculate Custom Summaries Based on Predefined Summaries](/WPF/images/WPF_Grid_CustomSummaries_PredefinedSummaries.png) - XAML

<dxg:GridControl ...
                 CustomSummary="grid_CustomSummary">
    <dxg:GridColumn FieldName="ProductName"/>
    <dxg:GridColumn FieldName="UnitPrice"/>
    <dxg:GridColumn FieldName="Quantity"/>
    <dxg:GridControl.TotalSummary>
        <dxg:GridSummaryItem x:Name="avgPrice" FieldName="UnitPrice" SummaryType="Average"/>
        <dxg:GridSummaryItem x:Name="avgQuantity" FieldName="Quantity" SummaryType="Average"/>
        <dxg:GridSummaryItem ShowInColumn="ProductName" SummaryType="Custom" 
                             DisplayFormat="{}Average order: {0:c}"/>
    </dxg:GridControl.TotalSummary>
    <dxg:GridControl.View>
        <dxg:TableView ...
                       TotalSummaryPosition="Bottom">
        </dxg:TableView>
    </dxg:GridControl.View>
</dxg:GridControl>

- C# - VB.NET

private void grid_CustomSummary(object sender, DevExpress.Data.CustomSummaryEventArgs e) {
    if (e.IsTotalSummary) {
        switch (e.SummaryProcess) {
            case DevExpress.Data.CustomSummaryProcess.Start:
                e.TotalValueReady = true;
            break;
            case DevExpress.Data.CustomSummaryProcess.Finalize:
                var averagePrice = (decimal)grid.GetTotalSummaryValue(avgPrice);
                var averageQuantity = (decimal)grid.GetTotalSummaryValue(avgQuantity);
                e.TotalValue = averagePrice * averageQuantity;
            break;
        }
    }
}

Private Sub grid_CustomSummary(ByVal sender As Object, ByVal e As DevExpress.Data.CustomSummaryEventArgs)
    If e.IsTotalSummary Then

        Select Case e.SummaryProcess
            Case DevExpress.Data.CustomSummaryProcess.Start
                e.TotalValueReady = True
            Case DevExpress.Data.CustomSummaryProcess.Finalize
                Dim averagePrice = CDec(grid.GetTotalSummaryValue(avgPrice))
                Dim averageQuantity = CDec(grid.GetTotalSummaryValue(avgQuantity))
                e.TotalValue = averagePrice * averageQuantity
        End Select
    End If
End Sub

You can use the [e.GetGroupSummary](/CoreLibraries/DevExpress.Data.CustomSummaryEventArgs.GetGroupSummary%28System.Int32-System.Object%29) method to obtain predefined group summary values. ## Specify Whether to Calculate Summaries The [CustomSummaryExists](/WPF/DevExpress.Xpf.Grid.GridControl.CustomSummaryExists) event or the [CustomSummaryExistsCommand](/WPF/DevExpress.Xpf.Grid.GridControl.CustomSummaryExistsCommand) property allows you to specify which summaries should be calculated and displayed. The following example calculates group summaries only for the top group level: ![DevExpress WPF | Grid Control - Custom Summary Exists](/WPF/images/GridControl_CustomSummaryExistsCommand.png) [View Example: How to Display Group Summaries](https://github.com/DevExpress-Examples/wpf-data-grid-display-group-summaries) - MainWindow.xaml

<dxg:GridControl x:Name="grid"
                 ItemsSource="{Binding AccountList}"
                 CustomSummaryExistsCommand="{Binding CustomSummaryExistsCommand}">
                 <!-- ... -->
    <dxg:GridControl.GroupSummary>
        <dxg:GridSummaryItem FieldName="Age" SummaryType="Min"/>
        <dxg:GridSummaryItem FieldName="Age" SummaryType="Max"/>
    </dxg:GridControl.GroupSummary>
</dxg:GridControl>

- MainViewModel.cs - MainViewModel.vb

using DevExpress.Mvvm;
using DevExpress.Mvvm.DataAnnotations;
using DevExpress.Mvvm.Xpf;
// ...
public class MainViewModel : ViewModelBase {
// ...
    [Command]
    public void CustomSummaryExistsCommand(RowSummaryExistsArgs args) {
        args.Exists = args.GroupPath[0].GroupLevel == 0;
    }
}

Imports DevExpress.Mvvm
Imports DevExpress.Mvvm.DataAnnotations
Imports DevExpress.Mvvm.Xpf
' ...
Public Class MainViewModel
    Inherits ViewModelBase
' ...
    <Command>
    Public Sub CustomSummaryExistsCommand(ByVal args As RowSummaryExistsArgs)
        args.Exists = args.GroupPath(0).GroupLevel = 0
    End Sub
End Class